linux-kernel - Re: [PATCH 1/2] staging: lustre: lprocfs: Use kstrtouint_from

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Message-ID: <20170518111343.15a263f1@alcyone.localdomain>
Date:   Thu, 18 May 2017 11:13:43 -0400
From:   Mathias Rav <mathiasrav@...il.com>
To:     "Dilger, Andreas" <andreas.dilger@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "Drokin, Oleg" <oleg.drokin@...el.com>,
        James Simmons <jsimmons@...radead.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        Lustre Development List <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH 1/2] staging: lustre: lprocfs: Use kstrtouint_from_user

On Thu, 18 May 2017 14:48:25 +0000
"Dilger, Andreas" <andreas.dilger@...el.com> wrote:

> On May 18, 2017, at 15:53, Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:
> > 
> > On Thu, May 04, 2017 at 12:13:38PM -0400, Mathias Rav wrote:  
> >> Prefer kstrtouint_from_user to copy_from_user+simple_strtoul.
> >> 
> >> The helper function lprocfs_wr_uint() is only used to implement
> >> "dump_granted_max" in debugfs.
> >> 
> >> Note the slight change in semantics: The previous implementation using
> >> simple_strtoul allows garbage after the number, whereas kstrtox only allows
> >> a trailing line break. The previous implementation allowed a write of zero
> >> bytes whereas kstrtox will return -EINVAL. Since this only affects a single
> >> debugfs endpoint, this should be a permissible slight change of semantics
> >> in exchange for 18 fewer lines of code.
> >> 
> >> Signed-off-by: Mathias Rav <mathiasrav@...il.com>
> >> ---
> >> .../lustre/lustre/obdclass/lprocfs_status.c        | 22 +---------------------
> >> 1 file changed, 1 insertion(+), 21 deletions(-)
> >> 
> >> diff --git a/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c b/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
> >> index 1ec6e3767d81..338ce34d6514 100644
> >> --- a/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
> >> +++ b/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
> >> @@ -399,27 +399,7 @@ EXPORT_SYMBOL(lprocfs_rd_uint);
> >> int lprocfs_wr_uint(struct file *file, const char __user *buffer,
> >> 		    unsigned long count, void *data)
> >> {
> >> -	unsigned *p = data;
> >> -	char dummy[MAX_STRING_SIZE + 1], *end;
> >> -	unsigned long tmp;
> >> -
> >> -	if (count >= sizeof(dummy))
> >> -		return -EINVAL;
> >> -
> >> -	if (count == 0)
> >> -		return 0;
> >> -
> >> -	if (copy_from_user(dummy, buffer, count))
> >> -		return -EFAULT;
> >> -
> >> -	dummy[count] = '\0';
> >> -
> >> -	tmp = simple_strtoul(dummy, &end, 0);
> >> -	if (dummy == end)
> >> -		return -EINVAL;
> >> -
> >> -	*p = (unsigned int)tmp;
> >> -	return count;
> >> +	return kstrtouint_from_user(buffer, count, 0, (unsigned int *)data);  
> > 
> > Why not just delete this whole function and have the callers make this
> > call instead?  No need for unneeded wrapper functions of core kernel
> > calls.  
> 
> Even better, it looks like this function has no callers on the client and could just
> be deleted entirely.

No, the functions lprocfs_{rd,wr}_uint are used once through a macro:
ldlm/ldlm_resource.c calls LPROC_SEQ_FOPS_RW_TYPE(ldlm_rw, uint)
to define ldlm_rw_uint_seq_{show,write}, which then calls
lprocfs_{rd,wr}_uint which in turn call seq_printf/kstrtouint_from_user.

It seems like much indirection for almost no gain besides hiding
access to ((seq_file *) file->private_data)->private in a macro.

If you agree, I will prepare a patch that switches ldlm_resource to
using the LPROC_SEQ_FOPS macro directly, which allows us to remove two
trivial wrappers.

/Mathias